This invention relates to focal plane shutters for cameras, and more particularly to a control device for terminating the running down of the shutter blades.
When controlling the exposure by the use of a focal plane shutter, as the running down of the leading or trailing blades of the shutter is terminated, a bound or irregular motion of the shutter blades is apt to occur, causing not only the production of an unevenness in the exposure, or the like, but also damages of the shutter mechanism. Therefore, a wide variaty of bound preventing devices have so far found their use with the shutter of the type described above, and may be divided to two main classes, one of which is characterized by the braking action of frictional force, and the other by the use of an arresting member arranged to be actuated just before the blades bound. In the former braking device, the braking action operates gradually so that the life-time of the shutter mechanism is hardly shortened. But, since, during the film winding operation, the braking device reacts in a direction opposite to that in which the film winding proceeds, the driving torque tends to increase. Particularly with the electromagnetically operated shutter, as the driving force of running down the shutter blades is relatively weak, it is difficult for such electromagnetic drive source to accomplish the returning movement of the shutter against this braking force, unless the power of the drive source is greatly increased.
The latter device using the arresting member though having an advantage that the shutter can be returned with ease provided that this arresting member is released, will often damage the endurance of the shutter mechanism because the arresting member suddenly stops the shutter blades.